1. Field of the Invention
The present invention relates to a dispersion agent for cement (hereinafter, cement dispersion agent) capable of providing an excellent dispersibility without causing an alkali-aggregate reaction. The present invention also relates to a cement dispersion agent capable of improving the flowability of a cement mix such as cement paste, mortar, and concrete and of preventing the decrease in the flowability over a period of time when incorporated therein.
2. Description of the Related Art
Cement dispersion agents are formulated into cement mixes such as cement paste, mortar, and concrete to improve the dispersibility thereof and to reduce the water content in the mixes. Naphthalene sulfonic acid-formaldehyde condensate products are used at present in the art as such cement dispersion agents, but completely satisfactory effects have not been obtained from these products.
Further, problems have arisen because of alkali-aggregate reactions caused by fluctuations in the content of recently supplied concrete aggregate materials. These alkali-aggregate reactions cause expansion after construction, generating cracks, etc., in the cement mix products. The use of low alkali cement or good quality aggregate material has been proposed to inhibit these alkali-aggregate reactions, but low alkali cement is expensive and increases construction costs and a supply of good quality aggregate materials cannot be always ensured. Thus, this proposal is not practical.
No. JP-A-60-235756 (Kokai) proposes a method of producing the calcium salts of aromatic sulfonic acid-formaldehyde condensate products, since the amount of alkali metals present in cement distribution agents can not be ignored as a factor contributing to the alkali-aggregate reactions. However, the properties of these cement distribution agents are not satisfactory, as mentioned above.
The use of polyethylene sulfonates or the copolymers thereof as a cement distribution agent is disclosed in, for example, No. JP-A-51-525, 57-156355, and 60-46956 (Kokai) and U.S. Pat. No. 4076699. The calcium salt is disclosed as one of the salts therein, but no teaching as to the alkali-aggregate reaction is mentioned. Furthermore, although No. JP-A-51-525 teaches that, since the low sulfonation degree of polystyrene sulfonates exhibits hydrophobic properties, which cause an insufficient initial dispersibility and unsatisfactory strength improvement, an average substitution of 0.5 or more, preferably 0.7 or more, based on one styrene group, of a sulfonic acid group is recommended. However, the effects obtained from the use of the higher sulfonation degree are not taught at all in this reference.
Quality control requirements have recently become severe, in line with the increased large scale use of, for example, cement, concrete, and mortar. Accordingly, the use of ready mixed concrete, which is transported in large amounts and over long distances by special vehicles from the concrete production plants, has remarkably increased. During such transportation, however, a so-called "slump loss" phenomenon occurs in the ready mixed concrete, i.e., the flowability of the ready mixed concrete is reduced with the elapse of time because the cement particles coagulated when a certain time has elapsed after mixing. This phenomenon is particularly remarkable when naphthalene sulfonic acidformaldehyde condensate dispersion agents are used. Furthermore, although the amount of water in a concrete mix should be decreased to increase the strength of concrete, a reduction in the water content accelerates the generation of the "slump loss" phenomenon.
Accordingly, the ready mixed concrete to be transported by a special vehicle is adjusted, during the production thereof, so that it has a suitable flowability from the viewpoint of workability at a construction site. However, there are technical limitations to the amount of adjustment that can be made as is known in the art. Further, even when the above-mentioned adjustment is made, the time required for transportation varies with each special vehicle, due to variances in transportation time, traffic conditions, and waiting time in the case of a large scale placing of concrete. When the "slump loss" is large, the pumping of the ready mixed concrete becomes difficult and causes problems Furthermore, since the ready mixed concrete has a poor flowability during placing, voids are formed in the concrete and various other disadvantageous inconveniences occur. For example, the load during compaction by a vibrator become increased, and the finish is non-uniform. Also in the cases of production of concrete molded articles such as concrete plates, concrete piles, etc., the "slump loss" may cause the production of non-uniform and off-spec products.
Various proposals have heretofore been made of additives, and the addition methods thereof, for improving the flowability of concrete mixes.
For example, it was proposed in No. JP-B-61-27344 (Kokoku) to prevent the decrease in the flowability with the elapse of time by adding gluconic acid salts to salts of naphthalene sulfonic acid-formaldehyde condensate products. However, a large amount of these additives must be used, and the effects obtained therefrom are still unsatisfactory.
It has been also proposed to prevent the decrease in the flowability with the elapse of time at a low temperature by adding malates (see No. JP-A-58-2249) or citrates (see No. JP-A-58-2250) to naphthalene sulfonic acid-formaldehyde condensate products. However, these references do not report that, at an ambient temperature or at an elevated temperature, a remarkable decrease in the flowability occurs with the elapse of time.
Furthermore, Nos. JP-A-51-525 and 56-41866 report the addition of polystyrene sulfonates to cement mixes as a dispersion agent. However, although polystyrene sulfonate dispersion agents improve the flowability, there is still a problem in that there is still a remarkable decrease in the flowability with the elapse of time.